1. Field of the Invention
The present invention relates to a linear guide apparatus provided with infinite circulating paths of rolling balls interposed between a guide rail and a slider movable on the guide rail, and in particular, to the linear guide apparatus improved to obtain an operational performance with high accuracy.
2. Description of the Relevant Art
A linear guide apparatus of this type is disclosed, for example, in U.S. Pat. No. 4,472,003. In this linear guide apparatus, as shown in FIGS. 1 and 2 of this application, a slider 4 is formed with an axial recess 1. A pair of axial ball rolling grooves 2 are formed in the inner surfaces of the axial recess 1, and axial through holes 3 are bored at lateral positions with respect to the ball rolling grooves 2. An elongate guide rail 9 has axial ball rolling grooves 8, respectively, opposing the ball rolling grooves 2 of the slider 4. End caps 6 are respectively secured to opposite ends of the slider. Each of the end caps 6 has a semicircular ball path (curved ball groove) 5 for connecting the mutually opposing ball rolling grooves 2 and 8 to the through hole 3 of the slider 4. A multiplicity of balls 7 are rollably inserted between the opposing ball rolling grooves 2 and 8, through holes 3, and semicircular ball paths 5.
The guide rail 9 is secured to a mounting base (not shown) by a bolt inserted through a bolt hole 10. The end caps 6 are attached to the slider 4 by screws 12 which are threaded into threaded holes 11 formed in end faces of the slider 4. The numeral 13 designates a threaded hole for fixing an article to the slider 4.
When the slider 4 moves in the axial direction on the guide rail 9, relative to the latter, the ball 7 rolls and circulates through the through hole 3, semicircular ball path 5, and between the ball rolling grooves 2 and 8 thereby enabling the slider 4 to travel smoothly.
However, in manufacture, it is difficult to accurately position the center of the circular arc defining the semicircular ball path 5 at the joining end face of the end cap 6 to the slider 4. Accordingly, the opposite end portions of the semicircular ball path 5 are not necessarily coincident with the ends of the semicircle of end cap 6. As a result, stepped portions will be formed in the ball circulating path at the joining planes between the slider 4 and the end cap 6. The balls 7, within the semicircular ball path 5, are moved by subsequent balls and, since the semicircular ball path 5 is curved outwardly, the balls 7 move while being pressed against the outside inner wall of the ball path 5. Furthermore, when the slider 4 travels at high speeds, the balls 7 will be further pressed against the outside inner wall surface by a centrifugal force exerted to the balls 7. These pressing forces, imparted to the balls 7, are gradually decreased as the balls 7 approach the straight through hole 3, and the forces become zero when the balls 7 reach a position in the through hole 3 which is spaced from the entrance thereof by a distance corresponding to the diameter of the balls 7. For this reason, at the joining portion A between the semicircular ball path 5 and the ball through hole 3 of the slider 4, the balls 7 passing through this portion A are pressed against the stepped portion in the ball circulating path. Consequently, if such a stepped portion is formed at this joining portion, even a slight step, ball circulation will be disrupted and vibrations will be caused.
In particular, in those linear guide apparatus used for hard disk driving devices and the like, which are required to be operated with extremely high accuracy, the diameter of the balls 7 are as small as 2 mm. Thus, any influence caused by even a minute error in dimension will pose a serious problem.